The present invention relates to an optical communication system; and, more particularly, to an optical switch for selectively transmitting an optical signal to one of multiple optical paths.
Generally, an optical communication system has been used for achieving a high rate of data transmission performance by using optical fibers. For example, information in the fiber optic communication system may be sent in the form of optical pulses at a rate of 100 to 2,500 megapulses per second. In general, to change directions of optical transmissions a switch for use in the optical communication system has M numbers of inputs and N numbers of outputs, wherein both M and N are positive integers.
FIG. 1A is a layout of a prior art optical switch, which represents a 2xc3x972 matrix structure having two inputs and two outputs.
Referring to FIG. 1A, actuators are provided with mirror surfaces 13a to 13d, which are located at an end of each actuator and inclined at a 45-degree angle. Each of the mirrors is capable of reflecting a light incident thereon. In case when the actuators 111, 114 turn on and the actuators 112, 113 turn off, the first and the fourth mirror surfaces 13a, 13d are moved forward, thereby making lights from optical fibers 181, 182 travel to optical fibers 183, 184, respectively.
On the other hand, if the actuators 112, 113 turn on and the actuators 111, 114 turn off, the second and the third mirror surfaces 13b, 13c are moved forward, thereby making lights from optical fibers 181, 182 travel to optical fibers 184, 183, respectively, as shown in FIG. 1B.
As described above, there is a need for designing an array of Mxc3x97N actuators which is capable of transmitting optical signals emitted from M numbers of input optical fibers to other N numbers of output optical fibers. Each of the optical fibers 181, 182 includes a first groove 14-1 at an input terminal thereof to mount a first microlens 15 which collimates a light beam incident thereon. And each of the optical fibers 183, 184 includes a second groove 14-2 at output terminals thereof to mount a second microlens 16 which focuses a light beam incident thereon. The light beam from the second microlens 16 travels along a trench 17. At this time, it is required that an optical waveguide is used for reducing an optical loss due to the divergence of the light beam.
U.S. Pat. No. 5,208,880 issued to Liza et al., entitled xe2x80x9cMicrodynamical Fiber-optic Switch and Method of Switching Using samexe2x80x9d, discloses one of conventional optical switches including a mechanical support structure incorporating therein a piezoelectric material in the form of a ladder and a mirror. They are mechanically secured to the central portion of the support structure for modulating an optical path of a light beam incident on the mirror by applying an electric signal to the piezoelectric material. It takes advantage of the support structure to obtain a long operational distance by using a low voltage, however, it has a shortcoming that an accuracy of the position control of the mirror can be deteriorated.
U.S. Pat. No. 5,446,811 issued to Field et al., entitled xe2x80x9cThermally Actuated Optical Fiber Switchxe2x80x9d, discloses a micromachined device for selectively switching an optical fiber between first and second positions. The micromachined device includes a working leg and a second leg which has a cross-sectional area that is larger than that of a working leg, thereby presenting an electrical resistance difference between the working leg and the second leg to a current flow. The difference in electrical resistance provides a difference in thermal expansion so that the working leg deforms in the direction of the second leg. Therefore, if optical fibers are mounted on grooves formed on the legs and current flows to the legs, the structure serves as a 1xc3x97N optical switch. However, this structure suffers from large power dissipation since it employs a thermal actuating method. Further, since the legs cannot be linearly moved, it gives rise to angle deflection errors in the output optical fibers. In addition, it is impossible to make an Mxc3x97N optical switch because the number of the input optical fibers is limited to one.
U.S. Pat. No. 4,759,579 issued to Lemonde, entitled xe2x80x9cMechanical Switch for Optical Fiberxe2x80x9d, teaches an optical switch including a rigid arm in the form of a seesaw and a pair of superposed slabs. The rigid arm carries a moving optical fiber and each slab is provided with an alignment groove mounting thereon a fixed optical fiber. In this optical switch, the moving optical fiber is selectively coupled to fixed optical fibers according to the movement of the seesaw rigid arm. This structure has a high accuracy in aligning the optical fibers, however, it is limited to expand the number of the fixed optical fibers.
In an article of IEEE, Photonics Technology Letters, Vol. 10, No. 4, pp. 525-527, April 1998, entitled xe2x80x9cFree-Space Micromachined Optical Switches with Submilisecond Switching Time for Large-Scale Optical Crossconnectsxe2x80x9d, a mirror surface formed on a silicon surface changes an optical path by using Scratched Drive Actuator (SDA) which moves the mirror surface sanding normal to the silicon surface. However, this method needs 100 volts, 500 MHz operating voltage, and also needs a feedback control since inaccurate mirror positions due to the mirror wearing makes an optical path changed unnecessarily.
In an article of IEEE, Vol. 5, No. 4, pp. 231-237, December 1996, entitled xe2x80x9cElectrostatic Micro Torsion Mirrors for an Optical Switch Matrixxe2x80x9d, there is disclosed an optical switch which includes a mirror surface formed on a silicon surface with standing perpendicular to the silicon surface and a dummy substrate to secure the mirror surface attached thereto. Since, however, this optical switch has many obstacles in production. That is, it needs high, e.g., 100 volts and a temporary support in manufacturing processes.
In an article of IEEE, Vol. 5, No. 2, pp. 207-213, June 1998, entitled xe2x80x9cHigh-Aspect Ratio SI Vertical Micromirror Array for Optical Switchingxe2x80x9d, there is disclosed an optical switch which includes an actuator and a mirror attached to the actuator with standing perpendicular to a surface of the actuator. This method has a problem that the voltage must apply at least 50 volts to the actuator during OFF state.
In view of the above-described patents and papers, the conventional optical switches should be still improved in position accuracy, power dissipation, scalability and productivity.
It is, therefore, a primary object of the present invention to provide an improved optical switch with a latchup structure which is obtained by utilizing a leaf spring.
In accordance with the present invention, there is provided an optical switch for selectively changing an optical path of an optical signal for use in an optical communication, comprising: a mobile structure provided with a mirror surface at one side of the mobile structure to change the optical path by moving backward and forward the mobile structure along an axis parallel to the mirror surface; at least a pair of leaf springs in the form of a shallow arch, wherein the pair of leaf springs is connected to both sides of the mobile structure in a direction perpendicular to the mirror surface, respectively, thereby obtaining a latch-up function; and an actuator for moving the mobile structure.
Preferably, in order to give the degree of freedom to a leaf spring in the axial direction thereof and to reduce a critical force required in the reverse direction of the buckling, an elastic body is connected between the connection portions in perpendicular to the leaf spring, wherein the elastic body is selected from a group consisting of an I-shape beam, a multiple spring with a curvature and a S-shape beam allowing angle deflection.
And also, the mobile structure is made of a crystalline silicon or a polycrystalline silicon to secure high density and stability, and it is preferable that a sacrificial layer formed bottom of the mobile structure is made of silicon dioxide.
More preferably, a mirror surface is designed in the form of a concave lens in one dimension or in two dimension to reduce the divergence of optical signals, wherein the mirror surface is deposited with a metal selected from a group consisting of an aluminum, gold and nickel to effectively reflect the optical signal impinged onto the mirror surface